Construction
work at the Plan de Corones site. Double-layered external walls allow air
circulation for free cooling operation.

Click on the Image to Enlarge

BOLZANO,
Italy — While it is common for a transmitter site to be
located on the top of a mountain, it’s less common for one to be found
underground.

The Plan de Corones transmitting site is just that —located underground. It is situated on
the eponymous mountain plateau in the Italian province of South Tyrol in the
Alps, an area that once hosted many small lattice towers for TV, radio,
telephony and emergency rescue services.

From the RF planning point of view, the Plan de Corones
site benefits from a strategic location and can easily serve the more than 25,000
people living in the surrounding valleys.

SINGLE SITE
At first glance,
located 2,265 meters (7,430 feet) above sea level with some 100 assorted
antennas covering one 80-meter (260-foot) mast and no building in sight, one
might imagine that they are seeing a high-altitude monument to broadcasting.

“About 20 years ago, the South Tyrol Council envisioned
a single, high-end, transmitting facility to group together each existing
separate transmitting location,” said Daniel Largher, civil infrastructure
manager at RAS, which stands for Radiotelevisione Azienda Speciale
(Rundfunk-Anstalt Südtirol in German), South Tyrol’s public service
broadcaster.

A view of the nearly completed Plan de Corones site showing the enormous tower.

Click on the Image to Enlarge

The idea was to offer to any operator hosting services at
a competitive rate, according to a publicly available price list, and to
streamline operation while reducing the impact on the site’s surroundings. The
first step was to select a popular tourism location and get feedback from the
market about this prospective project. The council chose Masi della Muta, near
Merano, where more than 30 small lattices were spread throughout the petite
plateau. In 1996 it then commissioned the RAS to design and construct a transmission
facility to be shared among the various operators.

The Plan de Corones site is so carefully designed and
built, including RF coverage and operation reliability, that most operators in
the area found the new site to be a better alternative to any of the existing
“basic” individual sites.

“The new site proved that a publicly-owned entity could
hit the mark. Now at Masi della Muta there is just one transmitter site, and
the environmental impact has been greatly reduced. Cooling, UPSes and security
systems are shared as well, thus ensuring a high quality of service for each
operator at a fraction of the cost of corresponding individually-run systems,”
Largher said.

Plan de Corones Tower as of Late Summer 2013

Click on the Image to Enlarge

“In about 20 years we have built nearly 60 shared sites
in various locations within South Tyrol. But when it came to the Plan de
Corones project, our idea was to construct a real flagship. Just a few years
ago, you could see nearly 40 small lattices on this plateau. During peak ski
season you can expect to have about 23,000 people here, and we thought of
shifting radiating antennas to a higher position in order to lower RF pollution
at the ski run level.”

FLAGSHIP
Largher explained that they also concentrated on
aesthetics — “our flagship had to be good-looking and functional. In order to
build a future-proof site, capable of meeting present and future needs, we
designed several large equipment rooms. And we built it underground.”

The Plan de Corones technological building is spread
over 900 square meters (9,690 square feet) on a single level with various rooms
shared among companies, based on similar needs. In general the mobile telephone
operators are grouped together, the emergency rescue services together, as are
the broadcasters.

“We wanted the tower to pop out from the grass, so the
reinforced concrete walls of the underground building were designed and shaped
like beams to also serve as the tower’s foundation. The tower stands directly
at the center of the walls’ beams,” Largher said.

RAS Civil Infrastructure Manager Daniel Largher observes the site from the 63-meter-high balcony of the tower. In the background lies the Pustertal Valley.

The 80-meter tower is made of galvanized steel. The
internal spiral staircase allows engineers to easily lay cables and antenna feeders.
The staircase leads to the upper balcony, 63 meters above ground level. Its
railing permits engineers to move around with peace of mind.

An external staircase starts from the upper balcony and
leads to the top of the tower. The tower diameter is 3 meters, and is designed
to handle a wind speed on average of up to 145 kilometers per hour (calculated
over a period of 10 minutes) and 270 kilometers per hour peak wind speed. Radio
link operation is possible up to a wind speed of 180 kilometers per hour. Under
these conditions design displacement at 80 meters is 456 millimeters, explained
Largher. According to Johann Silbernagl, RAS technical director, they are
currently hosting eight FM, two DAB and 18 DVB-T transmitters from various
broadcasters, plus a number of emergency rescue services, mobile
telecommunication services and radio links.

“The Plan de Corones tower features an overall surface
for antenna installation of 258 square meters, but it’s nearly ‘sold out,’” he
said. “We could never have imagined that almost the entire available space on
the tower would be leased in just three years!”

One of the Transmitter Rooms Within the Underground Building

Click on the Image to Enlarge

GPS-FREE SFN OPERATION
DAB and DVB-T services are operated as SFN networks in
Italy. Like at any RAS site, the relevant time and frequency reference signals
(1PPS and 10 MHz) come from the Nimbra Time Transfer GPS-free synchronization
system by Net Insight. Time and frequency reference signals coming from a
single master clock are muxed into the same STM-1 links used for feeding the
various transmitters (both RAS and in some cases guest broadcasters) with the
content to be aired.

No on-site GPS is therefore required, and the entire
SFN network relies on the same time and frequency reference signals, thus
improving the stability of SFN networks and ensuring smooth operation.

The RAS
produced a time-lapse video documenting the entire construction process at Plan
de Corones site. Watch it here.

Davide Moro
reports on the industry for Radio World from Bergamo, Italy.

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